This invention relates to the riser system of an off-shore production well and more particularly to a new and improved swivel in the riser system.
Upon the completion of off-shore oil wells which include crude oil and gas, it is necessary to provide means for collecting and/or transferring the crude oil to tankers from the collection point of the completed wells. One proposed system for use in deep waters is a multi-line riser system which would include among other equipment a riser base for attachment to the sea floor or ocean floor, a plurality of determinate length risers, supply pipes, universal joints for connecting the risers and mouring buoys or top support buoys along with mechanisms for use in loading the output of the production into storage vessels or ships.
Early in the development of the recovery of crude oil from off-shore production facilities, fixed platforms were used in the recovery system only in shallow waters and as exploration extended into deeper waters, it was important to provide a platform with tension legs as in U.S. Pat. No. 3,934,528. The present invention is directed to the use of rigid columns and risers with a universal joint that couples the several rigid risers to provide an articulated column. A production riser or column is a series of vertically spaced supports interconnected by universal joints with one end of the column of risers connected to rigid or fixed base and the other end of the column of risers connected to a buoy. In use herein, the term "production" refers to a completed well or wells and is directed to the recovery of the crude oil or gas in contrast to the drilling for the crude oil or gas. The base of the risers serves as the collection point for the several wells that are producing. The riser supports a plurality of vertically extending pipe for conveying the oil. The universal joint connects the ends of the adjacent risers permitting articulation therebetween ans also supports the swivels that interconnect the rigid pipes from one riser to rigid pipes of an adjacent riser. The use of rigid flow lines such as pipes depends on the swivel joint to take up all the stresses and forces that are a result of the tremendous operating conditions of wave action, and unusual weather conditions. Flexible hoses are not suited for marine application because of the need for large diameters for transmission of fluids and the ability to withstand high pressures.
The swivel joint of the present invention has sealing means operative under high internal pressures that permits the joint to sustain very high thrust loads due to external forces while at the same time permitting continuous oscillating motions with freedom for rotation that can exceed 360.degree..